Modular hip joint prosthesis with adjustable anteversion

ABSTRACT

The present invention provides a modular hip prosthesis, and instrumentation for implanting the same, which has provision for varying the angulation between the stem portion and the trochanteral module portion by provision of connection means between the neck and stem which can be positioned or attached together in a variety of rotational positions. Variation of the angulation or anteversion is made possible in accordance with the present invention by virtue of the fact that the axis of the connection portion of the stem and neck is angularly offset from the axis of the body of the stem and neck, respectively. A further aspect of this invention is the provision of instrumentation for formation of a cavity for implantation of a prosthesis of this invention which is provided with indication means for indicating to the surgeon the optimum angle for assembly of the prosthesis of invention for implantation into a particular proximal femur.

This application is a continuation of copending application Ser. No.07/431,412 filed on Nov. 3, 1989 now U.S. Pat. No. 5,025,881.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to artificial joints and particularly to modularproximal femoral hip prostheses, and a method and instrumentation forimplantation of the same.

2. Description of the Prior Art

Various prostheses have heretofore been designed to replace one or bothcomponents of a ball and socket hip joint. Generally the ball portion isconnected to an arm composed of a neck and a stem or shaft which stem orshaft is embedded in the intramedullary canal of the proximal femur forhip reconstruction. Such prostheses are often formed with an integralstem and neck portion. Often a removable ball or head element ispositioned on the proximal end of the neck. See, for example, U.S. Pat.Nos. 4,012,795 or 4,459,708.

Recently the use of modular structures fitted together from a number ofreplaceable parts available in a variety of sizes have been used. Withsuch prostheses it is possible to replace either the head portion ortrochanteral portion of the prostheses, or both without removal of thestem from the bone cavity. U.S. Pat. Nos. 4,608,055, 4,676,797 and4,693,724 are all illustrative of such devices. The latter patent alsodiscloses the possibility that the angle at which the neck protrudesfrom the proximal end of the femur (referred to in said patent as"anteversion") may be adjusted without removal of the stem by pivotingthe neck on the end of the implanted stem. None of the prior art devicesof which applicant is aware provide any means for varying the anglebetween the axis of the trochanteral module and the axis of the stem sothat the actual angulation (sometimes referred to as anteversion) orslope of the proximal end of the femur may be duplicated by adjustmentof said angle.

The present invention provides a modular hip prosthesis, andinstrumentation for implanting the same, which has provision for varyingthe angulation between the stem portion and the trochanteral, or neck,portion by provision of connection means between the trochanteral moduleand stem which can be positioned or attached together in a variety ofrotational positions. Variation of the angulation or anteversion is madepossible in accordance with the present invention by virtue of the factthat the axis of the connection portion between the stem andtrochanteral portion is angularly offset from the axis of the body ofthe stem. The prostheses of this invention are further characterized bythe fact that no impediment exists to securing the stem and necktogether in a variety of rotational positions. Like other modularprostheses the hip joint prostheses of this invention provide theadvantage that either or both the ball component or trochanteral modulecomponent can be removed if replacement becomes necessary withoutextraction of the stem from the bone canal. Different size balls ortrochanteral components could also be substituted should the surgeondecide that such revision is necessary after a period of time.

A further aspect of this invention is the provision of instrumentationfor formation of a cavity for implantation of a prosthesis of thisinvention which is provided with indicia or markings for indicating tothe surgeon the optimum angle for assembly of the prosthesis ofinvention for implantation into a particular proximal femur. Theinvention further provides a novel method for determining the properangulation for a particular proximal femur using angulation readingstaken off of indicia provided on the rasp used to prepare the proximalfemur for the prosthesis. Such readings then provide a basis forassembly of the prosthesis in the correct orientation to fit theproximal femur.

Briefly summarized the present invention provides a modular hip jointprosthesis having provision for varying the angulation of the stemportion and the trochanteral module to coincide with the degree ofangulation in the proximal femur of a patient. The prosthesis includes aball, a stem component for implantation in a proximal femur, atrochanteral module adapted to be connected at its proximal end to saidball and at its distal end to said stem component by a connectionportion. The connection portions of the stem and trochanteral componentshave no mechanical impediment to limit securing the two componentstogether in a variety of rotational positions. The trochanteral modulecomponent is of an oblong cross-section on a plane perpendicular to thelongitudinal axis of its distal connection portion. It, further, issymmetrical in shape across the plane in which the axis of the ballconnection shaft is located, but is preferably non-symmetric in allother planes. Thus when the stem component is rotated in differentorientions relative to the trochanteral module, a tilting of thetrochanteral module occurs relative to the stem, making it possible toclosely match the natural tilt of the proximal femur. The stem componentis provided with a connection portion which, as already noted, mateswith the connection portion of the trochanteral module in a variety ofrotational positions, with the axis of the connection portion of thestem being angularly offset from the axis of the body of the stem. Theimplant is provided with markings or indicia positionedcircumferentially around the connection portion so that the surgeon canmatch the orientation of the implant with that of the instrumentation asobserved from the indicia thereon when the rasp portion of theinstrumentation is imbedded in the proximal femur.

The novel surgical instruments of this invention include a stemcomponent which has a connection portion offset at an angle identical tothe angle at which the connection portion of the implant stem is offsetfrom the axis of the implant stem. The instrument connection portion isadapted to receive a series of rasp block portions of progressivelyincreasing dimension. Each of the rasp block portions are of a shapecorresponding to the trochanteral modules of the implants. The raspblocks and the instrument connection portion each have markings thereonlocated circumferentially around the connection portion fordetermination of the relative orientation between the rasp block and thestem axis. The neck of the implant and connection portion of the implantstem have similar markings to allow the surgeon to assemble the implantin the same orientation as observed on the rasp instruments after theyhave been inserted in a manner and orientation deemed to be optimal bythe surgeon.

The novel method of the invention is as follows: the surgeon begins byremoving the head of the proximal femuri this resection being a roughresection. The surgeon then inserts a starter reamer into the medullarycanal of the femur and sequentially reams using reamers of progressivelyincreasing diameters until he finds a reamer of the appropriate diameterwhich contacts the cortical bone. The reamers employed are cylindricalin shape and have helical or longitudinal flutes which cut the bone.Once the appropriate diameter for the distal stem is thus determined bymeans of the reaming, the surgeon selects that same diameter distaltrial stem and assembles onto it a proximal rasp portion which mimicsthe geometry of the trochanteral module of the actual implant. Thedistal trial stem also corresponds to the geometry of the distal stem ofthe implant. The proximal rasp has a hole through it that has a centerline that is coincident in orientation to the center line of theconnection portion on the actual proximal wedge of the implant. Thetrial stem has a long cylindrical stud that projects proximally off ofthe distal stem at an angle that is the same angle as the connectionportion on the actual distal stem, but this stud is cylindrical and hasa length sufficient such that when assembled through the hole in theproximal rasp, the stud extends out of the other side of the proximalrasp and is then attached to the driving handle. The driving handleholds the entire assembly together by engaging the end of the stud onthe trial stem by means of an interlock mechanism. The entire assemblyis locked together such that the proximal rasp can rotate on the distalstem but is axially retained on the driving handle. The distal stem canfreely rotate about the center line of the stud axis, and the handle andproximal rasp may be locked together so that they rotate as one unit.Since the surgeon has already selected the distal trial stem by reaming,the only component that is changed during the sequential rasping is theproximal rasp. The surgeon begins with a small proximal rasp andprogressively utilizes larger rasps until he determines the size whichwill best fit the proximal region of the bone. During the raspingprocess the surgeon is free to rotate the proximal rasp relative to thedistal stem and thus determine an optimum orientation of the rasp. Hewill visualize the best position for the proximal rasp each time hedrives the proximal rasp down into the bone. When he finally reaches theappropriate size rasp he will leave the rasp and distal stem in the bonebut detach the driving handle so that he can see the top surface of therasp and the stud projecting out through the hole in the rasp. The studis provided with a line or other mark and the top surface of each raspadjacent the opening is provided with a series of lines or marks. Eachof these lines will be at approximately 111/2° (or some other selectedinterval) apart from each other to indicate to the surgeon theorientation of the rasp on the rasp stem. The implant trochanteralmodule and implant stem are provided with identical markings so that thesurgeon is able to assemble them in an orientation identical to thatwhich was observed between the rasp and rasp stem. Hence the amount ofanteversion in the actual implant when it is assembled is the same asthat which was determined by virtue of the rasping procedure. The lineson both the rasp and implant neck are marked with letters or numbers,for example, 1 through 9 or A through J, etc. The surgeon thus canobserve the designated orientation of the rasp and distal trial stem andassemble the prosthesis using the markings as a guide. The surgeon willthus assemble the distal stem onto the proximal wedge in the sameposition that was read off of the instrumentation, thereby insuring thatthe amount of angulation in the femoral implant is the same as theamount of angulation in the bone.

DRAWINGS

The invention will be explained more particularly with reference to theaccompanying drawings wherein

FIG. 1 is an elevational side view of a prosthesis of the presentinvention with the modular components detached from one another.

FIG. 2 is a side view of another embodiment showing a trochanteralmodule assembled to a stem.

FIG. 3 is a cross sectional view of the prosthesis of FIG. 2 taken alongline 3--3.

FIG. 4 is a side view of instrumentation for preparing a proximal femurfor implantation of a prosthesis of this invention with a broken awayfemur shown in cross section and with other components broken away,

FIG. 5 shows the connection portion of the instrumentation in FIG. 4with parts broken away and with the handle portion shown in crosssection.

FIG. 6 is a top view of the rasp shown in FIGS. 4 and 5 with a trialstem having a marking thereon used in conjunction with said rasp shownremoved therefrom with an end broken away, and,

FIG. 7 is a prospective view showing a typical proximal femur and aprosthesis of this invention in a side by side relationship illustratingthe version between the central and proximal parts of a femur and animplant for said femur.

Referring to the drawings, there is seen in FIG. 1 a hip prosthesis 10which consists of a stem component 12 a trochanteral module 14 and aball or head portion 16. Stem 12 and module 14 are adapted to beconnected together be means of male taper connection 18 and a matingfemale taper connection 20, preferably of the Morse taper type. Head 16is similarly connected to neck portion 14 by means of friction fittapers 22 and 24. A pair of notches 23 or similar means is provided ontrochanteral module 14 to permit removal of the module from stem 12 ifrevision of the implant becomes necessary. Module 14 may be providedwith a shoulder 26, which is intended to rest on the end of the resectedfemur. A shoulder 26 is generally provided on at least the medial sideof the implant. Stem 12 is provided with a lower elongated portion 13which is offset angularly from connection portion 18. Flutes orindentations 15 may optionally be provided in the implantable stemportion 13, to form channels for receiving bone cement or macro boneingrowth. An extraction groove 17 is provided to facilitate removal ofthe stem should it become necessary.

In the embodiment of FIG. 2 trochanteral module 14 is depicted with aslightly differing configuration or outline in which the lateral aspectof said trochanteral component and a stem are parallel to an imaginaryline 66. Stem 112 has a lower portion 113 and flutes 115 similar tothose shown in FIG. 1. The Morse tapered cone 118 is provided with analternative end configuration with a circling indentation 119 whichprovides an alternative means for the surgeon to grasp the end of thestem module for removal if necessary.

As seen in FIG. 3 the bottom surface of the trochanteral module isprovided with markings 30 which indicate possible different rotationalorientations, markings 30 being radially positioned around thecircumference of the Morse taper opening 20. Stems 12 and 112 areprovided with a single mark 32 which can be placed in alignment with adesired mark selected from among 30 on the trochanteral marking. Pairsof markings 30 and 32 thus provide an indication to the surgeon of therelative orientation between the parts.

As seen in FIG. 6, similar markings are present on the surface of raspblock 46 said markings being indicated by numeral 54. As seen in FIG. 4,a trial stem 40 having dimensions similar to implant stem 13 is placedin the intramedullary canal of proximal femur 38 after resection of theproximal femur and drilling and reaming of the intramedullary canal toopen the cavity of sufficient diameter and depth to accommodate thetrial stem 40, which generally has a rounded lower end 42 to promoteease of insertion. Rasp wedge 46 is provided with cutting teeth 48. Asalready noted, a series of rasp wedges 46 of increasing size areprovided with the instrumentation. Each rasp wedge is provided with anopening to accommodate attachment stud 44 which is integral with trialstem 40. Attachment stud 44 is provided with a reference mark 53 bestseen in FIG. 6 at the top of each rasp wedge 46 is imprinted a series ofindicia 54 positioned circumferentially around a portion of opening 47.Indicia 54 coincide with the indicia 30 on the trochanteral module ofthe actual implant 14. As seen from FIGS. 2, 3, 4 and 6, indicia 30 onthe implant are positioned on the medial side of the trochanteralmodule. The corresponding markings on the rasp are positioned on thelateral side of the rasp wedge 46. In this way the markings willcoincide even though the markings on the implant are on the distal sideof the trochanteral module while the markings on the rasp wedge are onthe proximal side thereof. While this placement is preferred it will beapparent to those skilled in the art that the markings could be placedmedially on the rasp wedge and the order of reading of the numerals orindicia be reversed so that reading on the wedge would have to be fromright to left and on the trochanteral module from left to right. Howeverthe arrangement shown in the drawings is preferred since it promotesease of reading and minimization of error in reading and placement ofthe parts.

As previously noted each time the surgeon uses a progressively largerrasp wedge 46 to enlarge the opening in the proximal femur 38, he willuse his professional judgement to align the rasp wedge radially aroundthe attachment stem 44 to a position which in his judgement bestapproximates the opening in the femur which is of course determined bythe version angle B of the femur as seen in FIG. 7. The angle B beingthe relative displacement between the axis of the body of the femur andthat of the neck of the femur. Once the cortical bone has been removedby rasping to the surgeons satisfaction, rasp handle 50 is removed sothat the relative position between marking 53 and indicia 54 isobservable. The surgeon can then assemble the trochanteral module 14onto implant stem 13 in a position matching the orientation observedbetween the attachment stud 44 and rasp wedge 46. In other words mark 32is placed at the same position relative to indicia 30 as mark 53 wasobserved to be relative indicia 54.

As seen in FIG. 4, rasp handle 50 is provided for use in rasping thecancellous bone from femur 38. Rasp handle 50 has a flattened uppersurface 56 against which a hammer 52 may be struck to cause teeth 48 toremove some of the cortical bone. The mechanism for releasably attachingrasp handle 50 to the attachment stud 44 of the trial stem 40 is bestviewed in FIG. 5. As noted, an engagement groove 45 encircles attachmentstud 44 near its end. Engagement groove 45 is adapted to receive balls60 and 62 which are positioned in a sleeve portion of the distal end ofthe rasp handle 50 a slidable sleeve 58 encircles the distal end of therasp handle as seen in FIGS. 4 and 5. The distal inner portion of sleeve58 is provided with a portion of enlarged inner radius 61 which allowsballs 60 and 62 to move radially outward when sleeve 58 is raised to theposition shown in FIG. 5. Sleeve 58 is provided with outwardlyprojecting proximal end 59 to permit manual raising and lowering ofsleeve 58. When sleeve 58 is in its lowered position shown on FIG. 4 theballs are forced into engagement groove 45 to couple rasp handle toattachment stud 44. Rasp handle 50 can easily be removed from attachmentstud 44 by moving the sliding sleeve 58 upward thus allowing balls 60and 62 to move outwardly out of the engagement groove 45. An internalspring or similar means 64 is provided to urge sleeve 58 into the lockedposition illustrated in FIG. 4. A pin 65 or similar surface forengagement of spring 64 is provided to enable transfer of the springsforce to sleeve 58.

As seen in FIG. 7 the desirable orientation of implant 10 is such thatthe angle B between stem axis 70 and neck axis 71 is the same as angle Bbetween the hip stem 68 and head 69. Such alignment is achieved byvirtue of positioning achieved as indicated in FIG. 3.

While I have described certain specific embodiments of the invention forillustrative purposes, various modifications will be apparent to thoseskilled in the art which do not constitute departures from the spiritand scope of the invention as defined in the appended claims.

What is claimed is:
 1. A modular hip joint prosthesis comprising:a ball;a stem component having a longitudinal first axis and terminating inopposite proximal and distal ends, said proximal end configured with afirst connection portion and defining a second axis which forms anobtuse angle with the longitudinal axis; a trochanteral module componenthaving a neck element extending outwardly from a proximal portionthereof and a distal portion configured with a second connection portionfor mating engagement with said first connection portion, saidtrochanteral module defining a shape generally corresponding to that ofthe trochanteral portion of the proximal femur and connecting with saidstem in a variety of rotational positions; and means or the prosthesisfor indicating to a surgeon the relative rotational alignment betweenthe trochanteral module and the stem corresponding to the naturalanteversion angle of the femur.
 2. The prosthesis of claim 1 whereinsaid obtuse angle is complementary to an acute angle between 5 and 45degrees.
 3. The prosthesis of claim 1 further comprising a series ofindicia marks circumferentially oriented around each of said first andsecond connection portions, respectively, indicating the relativealignment of said, trochanteral module and said stem.
 4. The prosthesisof claim 1 wherein said first connection portion is a tapered cone andsaid second connection portion is a mating female tapered cone.
 5. Theprosthesis of claim 1 wherein each of said first and second connectionportions further comprise a planar abutting surface that isperpendicular to the axes of said connecting portions.
 6. The prosthesisof claim 1 wherein said trochanteral module defines a generallyasymetrical cross-sectional shape.